In optical pickup devices that perform recording/reproducing on/from optical disks, conventionally, laser diodes that emit a CD (Compact Disk) infrared laser with central wavelength of 800 nm and a DVD (Digital Versatile Disk) red laser with central wavelength of 650 nm have been used. In recent years, optical pickup devices that perform high-density recording using a BD (Blu-ray Disk) laser with central wavelength of 405 nm are put to practical use. A market of optical disk devices having optical pickup devices for BD grows.
However, at a stage that BD, DVD and CD coexist, it is necessary that one optical disk device enables recording/reproducing on/from plural kinds of optical disks with different wavelengths.
A diameter of a spot focused on a recording surface of an optical disk is different between a DVD/CD laser and a BD laser. Since a refractive index of an optical member such as an objective lens varies with wavelengths, one optical system cannot be directly shared. Therefore, individual optical systems are set for respective wavelengths, thereby realizing the recording/reproducing on/from plural kinds of optical disks.
However, in a case of an optical disk device to be incorporated into an electronic device such as a laptop personal computer that requires further miniaturization, weight saving and thinning, a strenuous demand is made such that a recording/reproducing mechanism for BD should be added and housed in a space equivalent to a space for a conventional optical disk device for DVD/CD. However, it is difficult to provide an optical system for recording/reproducing on/from BD separately from a conventional mechanism into a narrow space.
Therefore, a suggestion that a part of the optical system is shared and thus a space is saved is made.
FIG. 3 is a schematic diagram illustrating a basic configuration of an optical system of a conventional optical pickup device. As shown in FIG. 3, in conventional optical pickup devices, at the time of recording/reproducing on/from CD or DVD, DVD/CD laser diode 401 emits a dual-wavelength laser for recording/reproducing on/from DVD or CD. Outward light of the dual-wavelength laser for DVD/CD is transmitted through optical member 402. The outward light is transmitted through beam splitter 405, 80% or more of the outward light is reflected by DVD/CD reflective plate 406, and is transmitted through optical part 407 so as to be sent to DVD/CD objective lens 408. Particularly in a case of recording, 20% or less of the outward light is transmitted through DVD/CD reflective plate 406, and an approximately entire quantity of the outward light is transmitted through BD laser reflective plate 410 so as to enter light receiving element 415 used for controlling a laser power.
Optical part 407 has an aperture filter, a polarization hologram, and a quarter wavelength plate. The aperture filter realizes a necessary number of apertures that is compatible with DVD and CD. The polarization hologram reacts to DVD light. The quarter wavelength plate generates a phase difference of a quarter wavelength for outward light. The outward light, that is polarized into circular polarized light by optical part 407 and is focused by DVD/CD objective lens 408, is emitted to optical disk 409. DVD/CD return light reflected from optical disk 409 follows the same route as that of the outward light, and is returned into linear polarized light by optical part 407. Since a polarization direction of the return light is perpendicular to that of the outward light, an approximately entire quantity of the return light is reflected from DVD/CD laser reflective plate 406, and is transmitted through beam splitter 405 similarly to the outward light. Since the polarization direction of the return light is perpendicular to that of the outward light, the return light is reflected by optical part 402 and is received by light receiving element 413.
On the other hand, in a case of recording/reproducing on/from BD, BD laser diode 403 emits a BD laser. Outward light of the BD laser passes through optical member 404. The outward light is reflected by a reflective surface of beam splitter 405. The outward light is transmitted through reflective plate 406 for DVD/CD, 80% or more of the outward light is reflected by BD laser reflective plate 410 and is transmitted through optical part 411 so as to be sent to BD objective lens 412. Particularly in a case of recording, 20% or less of the outward light is transmitted through BD laser reflective plate 410, and enters light receiving element 415 used for controlling a laser power.
Optical part 411 has a quarter wavelength plate for generating a phase difference of a quarter wavelength in BD light. The outward light, that is polarized into circular polarized light by optical part 411 and is focused by BD objective lens 412, is emitted to optical disk 409. BD return light, that is reflected from optical disk 409, follows the same route as that of the outward light, and is returned to linear polarized light by optical part 411. Since a polarization direction of the return light is perpendicular to that of the outward light, an approximately entire quantity of the return light is reflected from the BD laser reflective plate 410, and is transmitted through DVD/CD reflective plate 406 similarly to the outward light so as to be reflected from the reflective surface of beam splitter 405. Since the polarization direction of the return light is perpendicular to that of the outward light, the return light is reflected by optical member 404 and is received by light receiving element 413.
Such a configuration enables the recording/reproducing on/from optical disks compatible to DVD, CD and BD.